Display screen or portion thereof with a graphical user interface



The sole FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing my new design.

The broken lines illustrate the display screen or portion thereof and form no part of the claimed design. The broken lines illustrate portions of the graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 